Himalayan balsam (Impatiens glandulifera) is an invasive non-native species (INNS) introduced into the UK from the Western Himalayas in 1839. Introduced as an an ornamental garden plant, Himalayan balsam is Britian’s tallest growing annual plant, reaching heights of 10 feet and has pink flowers with a distinctive scent and charismatic, exploding seed heads.
Impacts
In the Tweed catchment, as in other parts of the UK, Himalayan balsam has spread rapidly, forming dense monocultures along riverbanks and shading out native species. As well as directly reducing biodiversity, by out-competing native plants for light and nutrients, Himalayan balsam also produces more nectar than any European plant species, luring pollinators away from native plants and thereby decreasing pollination rates. This dense monoculture dies back in the winter, leaving riverbanks bare and liable to erosion. Dead plant material can also can enter the river, increasing the risk of flooding.
Himalayan balsam control
Traditional control methods, such as hand-pulling and chemical control, have been ongoing in the Tweed catchment for many years and these can be effective if the management regime is sustained. Tweed Forum have some great volunteers in different areas of the catchment who have spent lots of time and elbow-grease removing Himalayan balsam in their local area – you can see some volunteers from the Peebles area opposite! If you would like to join our volunteer programme, please contact us on info@tweedforum.org.
Using a novel biological control
Tweed Forum have been working with CABI since 2016 to trial the effects of a novel biological control; releasing a co-evolved rust fungus pathogen that exclusively attacks Himalayan balsam, leaving native species unscathed. A species of rust fungus, (Puccinia komarovii var. glanduliferae) from the plant’s native range was discovered and was brought back to the UK and put through stringent laboratory testing to ensure it would not affect any native crop or horticultural species. The rust was approved for release by Defra in 2014.
The rust has been released at various sites in the Tweed catchment and ongoing monitoring investigations are conducted at specific times of the year to determine how the pathogen is affecting Himalayan balsam. The rust infection manifests itself indifferent ways, by affecting the growth of Himalayan balsam seedlings or by covering the leaf surface in brown pustules, both of which hinder the growth and spread of this INNS. The main goal of this project is not to eradicate Himalayan balsam but to suppress its ability to form monocultures, allowing native plants to co-exist and thrive again.
